Chemical aspects of iron oxide coagulation in water: Laboratory studies and implications for natural systems

Initial coagulation rates of colloidal hematite (-Fe₂O₃) particles (diameter less than 0.1 µm) were measured experimentally in well-defined laboratory systems at constant temperature. The relative stability ratio,W, was obtained at various ionic strengths in NaCl medium and at pH values in the range from 3 to 12. ExperimentalW values ranged from 1 to 10⁴ in various systems. The results delineate the roles ofspecific andgeneralized coagulation mechanisms for iron oxides. Among the specifically-interacting species (G _ads ⁰ >G _coul ⁰ ) studied were phosphate, monomeric organic acids of various structures, and polymeric organic acids. The critical coagulation-restabilization concentrations of specifically-interacting anions (from 10^–7 to 10^–4 molar) can be compared with the general effects of non-specific electrolyte coagulants (10^–3 to 10^–1 molar). The laboratory results are interpreted with the help of a Surface Complex Formation/Diffuse Layer Model (SCF/DLM) which describes variations of interfacial charge and potential resulting from variations of coagulating species in solution. Comparison of these laboratory experiments with observations on iron behavior in estuarine and lake waters aids in understanding iron removal mechanisms and coagulation time scales in natural systems.     

磁性矿物的磁学鉴别方法回顾

磁性矿物的组成和颗粒粒径的分布决定了岩石或沉积物的基本磁学性质及其所携带的天然剩磁在地质时期内的稳定性.由于自然界中磁性矿物的复杂性和多样性，如何有效的确定磁性矿物的成分和粒径分布一直是岩石磁学的基础和难点.本文对确定磁性矿物成分和粒径分布的常见方法进行了较为详细的总结和分析，并对常见磁性矿物在高温和低温下的磁学性质进行了详细的论述.最后对如何应用综合方法判定样品中的磁性矿物种类以及粒度分布进行了探讨.     

Distribution and significance of hydrothermal alteration minerals in the Tuzla hydrothermal system, Çanakkale, Turkey

Hydrothermal alteration zones have been investigated by X-ray diffraction, mineralogical–petrographical techniques, and geochemical analysis. Examination of cores and cuttings from two drill sites, obtained from a depth of about 814–1020 m, show that the hydrothermal minerals occuring in the rock include: K-feldspar, albite, chlorite, alunite, kaolinite, smectite, illite, and opaque minerals.In the studied area, silicified, smectite, illite, alunite, and opal zones have been recognized. These alteration mineral assemblages indicate that there are geothermal fluids, which have temperatures of 150–220°C in the reservoir.The distribution of the hydrothermal minerals shows changes in the chemical composition of the hydrothermal fluid, which are probably due not only to interaction with host rock, but also to dilution of the Na–K–Cl-rich hydrothermal fluid of the deep reservoir by cold sea water at shallow levels. Geochemical analyses of the solid and liquid phases indicate that the hydrothermal fluids of the Tuzla geothermal system are in equilibrium with alteration products.The tectonic structure of the studied area is caused by NW–SE and NE–SW directional forces. The volcanic rocks where hydrothermal zones are observed in the studied area are of Lower–Middle Miocene age comprise latite, andesite, dacite, rhyolite-type lavas, tuff, and ignimbrites.     

Mobilization of aluminium in the wathering profiles of the African surface in Malawi

Leaching of aluminium from the weathering profile of the African surface in Malawi was deduced from the chemistry of a vadose profile. Its loss occurs where congruent kaolinite dissolution results in saprolite collapse, leaving a weakly lateritized, sandy residual mantle. This leaching is a contemporary process, as shown by the precipitation of aluminosilicate evaporites in the dambos (seasonally waterlogged bottomlands). This paper presents the results of determinations, by ICP-OES and AAS-graphite furnace, of aluminium levels in groundwaters, examining the effects of a variety of pretreatments. Filtration (0.45 μm) substantially reduces the levels of total aluminium, showing it to be in particulate form. Subsequent acidification causes precipitation of < 0.45 μm forms of aluminium, further reducing the apparent levels to below ICP-OES detection limit. This is consistent with mobilization in organically bound forms which are destabilized at low pH, and accords with earlier work which showed that indigenous micro-organisms can cause dissolution of kaolinite. Organically bound mobilization provides an explanation for aluminium leaching at near-neutral pH in conjunction with the presence of silica in solution. The identification of this mechanism of kaolinite dissolution and aluminium evacuation from vadose profiles provides a realistic process for the levelling of extensive planation surfaces; the contingent collapse of the kaolinized saprolite would lower the interfluves, progressively narrowing the vadose zone until the landsurface approaches the planar form of the stable, regional water-table.     

新疆现代盐湖盐类矿物及有关成盐机制

新疆是我国现代盐湖主要分布区之一,蒸发岩矿物类型较全,现已发现有32种矿物,其中有近年新发现的数种矿物以及新类型盐湖——硝酸盐盐湖;对石膏晶形标型性进行了探讨;有关成盐机制概括为四个方面,将生物成盐纳入成盐理论。     

New aspects on the chemistry of aluminum in soils

Dissolution kinetics of minerals can be significantly inhibited by re-adsorbed aluminum. As a consequence of neutralization, polynuclear Al species may be formed in soil solutions. While re-acidification leads to decomposition of the polymers, further neutralization induces the formation of aggregates. The complexation of heavy metal ions with dissolved and aggregated Al polymers is illustrated as a potential factor influencing the chemical speciation of heavy metals in soils.     

In-situ investigation on growth and dissolution of crystals in aqueous solution

In-situ observation methods to investigate the physics involved in growth and dissolution processes of crystals in aqueous solution at ordinary temperature and pressure are described. The methods visualize insitu the phenomena relating to clustering of nanometer sized embryonic particles, the mass transport from bulk solution and from a crystal, the concentration gradient in the diffusion boundary layer and its distribution around a crystal, and spiral growth steps with height of one nanometer. The techniques measure at the nanometer scale the growth and dissolution rates of individual spiral growth hillocks and etch pits whose dislocation characters are identified in-situ.     

Preliminary study on active features of Fenghuangshan-Tianshui fault, West Qinling north boundary fault zone since the late of Late Pleistocene

2 Conclusion Fenghuangshan-Tianshui fault is a Holocene active fault. It laterally slips at the average rate of 1.1 mm/a during 6.4 ka and vertically slips at the average rate of 0.37 mm/a and 0.16 mm/a since the time 16.6 ka and 6.4 ka before respectively. Diaogoumeng-Dongjiawan segment has occurred an abrupt event in the period of 6.4 ka BP, which is assumed to be related to the 734 Tianshui M=7 earthquake, but further work is still necessary. Foundation item: Chinese Joint Seismological Science Foundation (198023).     

On the formation of dissolution pipes in Quaternary coastal calcareous arenites in Mediterranean settings

A large number of uniform cone‐shaped dissolution pipes has been observed and studied in Quaternary coastal calcareous arenites in Apulia and Sardinia (Italy) and Tunisia. These cylindrical tubes have a mean diameter of 52·8 cm and are up to 970 cm deep (mean depth for sediment‐free pipes is 1·38 m). They generally have smooth walls along their length, are perfectly vertical and taper out towards their bottoms. Their development is not influenced by bedding nor fractures. Sometimes their walls are coated by a calcrete crust. Their morphology has been studied in detail and their relationships with the surrounding rocks and with the environment have been analysed. The perfectly vertical development is a clear evidence of their genesis controlled by gravity. The depth of the dissolution pipes can be described by an exponential distribution law (the Milanovic distribution), strongly suggesting they developed by a diffusion mechanism from the surface vertically downward. We believe dissolution pipes preferentially form in a covered karst setting. Local patches of soil and vegetation cause infiltration water to be enriched in carbon dioxide enhancing dissolution of carbonate cement and local small‐scale subsidence. This process causes the formation of a depression cone that guides infiltrating waters towards these spots giving rise to the downward growth of gravity‐controlled dissolution pipes. A change of climate from wetter phases to drier and hotter ones causes the formation of a calcrete lining, fossilizing the pipes. When the pipes become exposed to surface agents by erosion of the sediment cover or are laterally breached the loose quartz sand filling them may be transported elsewhere. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental study of the semi‐active control of building structures using the shaking table

A magnetorheological (MR) damper has been manufactured and tested and a non‐linear model is discussed. The parameters for the model are identified from an identification set of experimental data; these parameters are then used to reconstruct the force vs. displacement and the force vs. velocity hysteresis cycles of the MR damper for the hysteretic model. Then experiments are conducted on a three‐storey frame model using impact excitation, which identifies dynamic parameters of the model equipped with and without the MR damper. Natural frequencies, damping ratios and mode shapes, as well as structural properties, such as the mass, stiffness and damping matrices, are obtained. A semi‐active control method such as a variable structure controller is studied. Based on the ‘reaching law’ method, a feedback controller is presented. In order to evaluate the efficiency of the control system and the effect of earthquake ground motions, both numerical analysis and shaking table tests of the model, with and without the MR damper, have been carried out under three different ground motions: El Centro 1940, Taft 1952, and Ninghe 1976 (Tangshan Earthquake in Chinese). It is found from both the numerical analysis and the shaking table tests that the maximum accelerations and relative displacements for all floors are significantly reduced with the MR damper. A reasonable agreement between the results obtained from the numerical analysis and those from the shaking table tests is also observed. On the other hand, tests conducted at different earthquake excitations and various excitation levels demonstrate the ability of the MR damper to surpass the performance of a comparable passive system in a variety of situations. Copyright © 2003 John Wiley & Sons, Ltd.     

The role of gypsum and/or dolomite dissolution in tufa precipitation: lessons from the hydrochemistry of a carbonate–sulphate karst system

The precipitation of freshwater carbonates (tufa) along karstic rivers is enhanced by degassing of carbon dioxide (CO₂) downstream of karstic springs. However, in most karstic springs CO₂ degassing is not enough to force the precipitation of tufa sediments. Little is known about the role of dissolution of gypsum or dolomite in the hydrochemistry of these systems and how this affects the formation of tufa deposits. Here we present a monitoring study conducted over a year in Trabaque River (Spain). The river has typical karst hydrological dynamics with water sinking upstream and re‐emerging downstream of the canyon. Mixing of calcium–magnesium bicarbonate and calcium sulphate waters downstream of the sink enhances the dissolution of carbonates and potentially plays a positive role in the formation of tufa sediments. However, due to the common‐ion effect, dissolution of dolomite and/or gypsum causes precipitation of underground calcite cements as part of the incongruent dissolution of dolomite/dedolomitization process, which limits the precipitation of tufa sediments. Current precipitation of tufa is scant compared to previous Holocene tufa deposits, which likely precipitated from solutions with higher saturation indexes of calcite (SIcc values) than nowadays. Limited incongruent dissolution of dolomite/dedolomitization favours higher SIcc values. This circumstance occurs when waters with relatively high supersaturation of dolomite and low SO₄^2? composition sink in the upper sector of the canyon. In such a scenario, the process of mixing waters enhances the exclusive dissolution of limestones, preventing the precipitation of calcite within the aquifer and favouring the increase of SIcc values downstream of the springs. Such conditions were recorded during periods of high water level of the aquifers and during floods. This research shows that the common‐ion effect caused by the dissolution of gypsum and/or dolomite rocks can limit [or favour] the precipitation of tufa sediments depending on the occurrence [or not] of incongruent dissolution of dolomite/dedolomitization. Copyright © 2016 John Wiley & Sons, Ltd.     

Clay minerals in the late Quaternary sediment of Tulare Lake,California: Implications for climate change,weathering, and erosion processes

The clay mineralogy of Tulare Lake sediment was examined to investigate hydroclimatic and environmental changes in the southern Sierra Nevada Mountains (SNM) since the most recent glacial maximum. Evolution of clay mineral assemblages elucidates significant changes in weathering, erosion, and hydroclimatic condition in the catchment. During the last glacial period (24.4–15.1 cal ka BP), low illite content implies less physical erosion of the granitic batholith rocks and a cold and arid environment in the southern SNM. Abrupt increases of illite content at 21.8–20.8 and 17.6 cal ka BP resulted from the glacier advances to the ablation zone and illite-rich glacier flour was transported down to the lake. The gradual increase of smectite induced by progressive depletion of illite-rich glacier flour from 17.6 cal ka BP toward the end of this period indicates climate was beginning to get warm and wet. From 11.9 to 5.3 cal ka BP, two warm and wet periods (10.7–9.4 and 8.2–5.2 cal ka BP) were characterized by high smectite/illite content ratios and low illite crystallinity values, suggesting intensive rainfall precipitation and more physical erosion in the highland and lowland catchment as well as more smectite formation in the terrace soils. Since the last glacial period, physical erosion, in comparison to the chemical weathering, was the dominant process responding to the hydroclimatic change in the Tulare Lake catchment. Moderate to weak chemical weathering was signified by the mostly low illite chemical weathering index of the core sediments. Such results suggest that vegetation cover in the southern SNM was low and limited.     

地震现场震情监视预报工作的回顾及展望

回顾了我国 30多年来的地震现场震情监视预报工作。该工作从目标角度考虑大致可分为二个不同的阶段, 1980年前主要是地震预报方法的探索, 而 1980年以后,更主要的是承担地震预报的社会服务。对我国赴国外地震现场的工作情况作了概述, 并提出了地震现场震情监视预报工作的可能前景。     

Climatic control of the assemblages of secondary clay minerals in the A-horizon of United States soils

The concentrations (per cent) of secondary clay minerals (mica, vermiculite, montmorillonite, chlorite and kaolinite) in the A-horizon of 99 soil sample sites were entered into a cluster program to determine the common clay mineral assemblages found in U.S. soils. Five major assemblages were identified with the most common assemblage consisting of mica, montmorillonite and kaolinite. A suite of climatic variables was determined for each of the 99 sites, including the water balance variables and Arkley's leaching index. A discriminant analysis was then used to predict the occurrence of a clay assemblage from the climate data. Sixty per cent of the sites could be correctly predicted, although not all assemblages could be predicted equally well; two assemblages could be predicted with 88 and 82 per cent accuracy. The precipitation of the wettest month and Arkley's leaching index accounted for most of the predictive power. Thus this study supports theoretical models which suggest that seasonal moisture supply is an important control of clay genesis and persistence. A residuals analysis indicated that many of the palaeosols in the data set and many of the soils from glacial parent materials possessed clay mineral assemblages not expected on the basis of modern climate.     

Chemical characterization of naturally weathered oil residues in the sediment from Yellow River Delta, China

With its close proximity to Shengli Oilfield, China’s second largest oilfield, the Yellow River Delta is at high risk for crude oil contamination. The massive oil discharge in oilfield may offer a chance for a natural experiment to investigate compositional changes of oil residues and study the stability of source- and weathering-dependent molecular parameters in oil residues after spills. The results demonstrate that the conventional diagnostic ratios, such as C₂₉20S/(20S + 20R), C₂₉/C₃₀H, C₃₀βα/αβ, C₃₁22S/(22S + 22R), C₂-DBTs/C₂-PHENs, C₃-DBTs/C₃-PHENs, DBT/MCHRY, CHRY/PHENs, are also valid for oil source identification even after extensive weathering of spilled oils in terrestrial environment, although some exceptions were encountered for extensively weathered sample. Moreover, the ratios of selected specific biomarkers (the oleanane index, the gammacerane index) have been developed and assessed as source indicators. Finally, we find that some maturity parameters based on alkyl naphthalenes and methyl phenanthrenes in petroleum geochemistry, such as the methylnaphthalene ratios (TMNr, TeMNr, PMNr), the methylphenanthrene ratios (MPI-1, MPDF), can be applied for the source identification and correlation at their lightly to moderately weathered stage.     

A study on the reaction kinetics of mineral surface adsorption in mix system

The experimental results on adsorption of ions pb²⁺, Zn²⁺ and Ag⁺ onto mineral surfaces in a mix system show that the reaction kinetics of adions adsorbed onto mineral surfaces was mainly controlled by their diffusion rates in solution. The concentration variations can be fit for the second-order rate equation with good determined coefficients r = 0.800 5—0.979 7. In the near neutral solution, the concentration of exchanged ions K⁺ and Na⁺ related to reaction time can be described by the fint-order rate equation with r = 0.855 7–0.997 7. Meanwhile, the complex diffusionexchange rate equation is suitable for describing the ca^{2 +} concentration variation, as ions Pb^{2 +} and Zn²⁺ were adions. Experimental data show that the amount of ions K⁺, Na⁺and Ca²⁺ release is much more than that of adion decrement in solution. This fact may suggest that the complexstion reaction of adions Pb²⁺, Z²⁺ and Ag⁺ with the mineral surfaces was the major reaction process while adions were not entering the phyllosilicate interlayers or CaCO₃ lattice to exchange the ions K⁺, Na⁺ and Ca²⁺ at room temperature. Project supported by the National Natural Science Foundation of China (Grant No. 49773206) and the Natural Science Foundation of Guangdong Province (Grant No. 960504)     

Characteristics and origins of primary fluids and noble gases in mantle-derived minerals from the Yishu area, Shandong Province, China

springerlink.com Studies of mantle fluids are currently one of the hot topics in the earth science, greatly contributing to re-vealing origins and evolutions of fluids. In general, the concept of mantle fluids refers to their active compo-nents, such as CO2, H2O, N2, etc., while the noble gases inert in chemical properties belong to another research system. Due to their marked differences in various fluid sources of the Earth[1], the isotopic sig-natures of He and Ar have been widely used a…     

Inferring the location of catchment characteristic soil moisture monitoring sites. Covariance structures in the temporal domain

Information shortage is a fundamental constraint in catchment hydrology that severely affects the possibilities for secure inference of the generic hydrologic landscape, as well as for secure validation of physically deduced distributed models. The introduction of databases with high enough spatiotemporal resolution to properly reflect generic hydrological catchment characteristics may therefore be considered as an inferential breakthrough. The work presented here is part of a project where observations from such an Australian catchment (the Tarrawarra) are utilised to estimate the discrepancy for individual soil moisture monitoring sites in reflecting generic catchment characteristics. With low enough discrepancy, observation sites may be considered as catchment characteristic soil moisture monitoring (CASMM) sites, thus capturing unbiased catchment characteristics and being well suited to represent the catchment in a monitoring effort. In this particular study, covariance structures in the temporal domain are inferred in order to enable subsequent enquiries regarding CASMM discrepancies. This is accomplished with ARMAX filters applied to the conditional auto- and cross-covariance structures that connect observations of soil moisture to the temporal variation of meteorology. The results suggest that weekly observations of Tarrawarra soil moisture are quite consistent realisations of first order auto-regressive processes, which means that the present state of soil moisture is generally acquired through the past week. With auto-correlative effects filtered out, cross-correlative meteorological effects on Tarrawarra soil moisture are identified and generally represented by the present week's accumulation of rainfall, the present week's accumulation of global radiation, and the previous week's maximum wind speed. After successive filtering of conditional cross-correlative effects, residual time-series observations may be considered as temporally independent, and therefore are well suited for subsequent inferences regarding covariance structures in the spatial domain. Since the exclusion of auto-correlative effects is necessary for unambiguous model interpretation, the estimated cross-correlative parameters should reflect the true nature of underlying physical processes.     

Movement and strain conditions of active blocks in the Chinese mainland

The definition of active block is given from the angles of crustal deformation and strain. The movement and strain parameters of active blocks are estimated according to the unified velocity field composed of the velocities at 1598 GPS stations obtained from GPS measurements carried out in the past years in the Chinese mainland and the surrounding areas. The movement and strain conditions of the blocks are analyzed. The active blocks in the Chinese mainland have a consistent E-trending movement component, but its N and S components are not consistent. The blocks in the western part have a consistent N-trending movement and the blocks in the eastern part have a consistent S-trending movement. In the area to the east of 90°E, that is the area from Himalayas block towards NE, the movement direction of the blocks rotates clockwisely and the movement rates of the blocks are different. Generally, the movement rate is large in the west and south and small in the east and north with a difference of 3 to 4 times between the rates in the west and east. The distributions of principal compressive strain directions of the blocks are also different. The principal strain of the blocks located to the west of 90oE is basically in the SN direction, the principal compressive strain of the blocks in the northeastern part of Qingzang plateau is roughly in the NE direction and the direction of principal compressive strain of the blocks in the southeastern part of Qingzang plateau rounds clockwisely the east end of Himalayas structure. In addition, the principal strain and shear strain rates of the blocks are also different. The Himalayas and Tianshan blocks have the largest principal compressive strain and the maximum shear strain rate. Then, Lhasa, Qiangtang, Southwest Yunnan (SW Yunnan), Qilian and Sichuan-Yunan (Chuan-Dian) blocks followed. The strain rate of the blocks in the eastern part is smaller. The estimation based on the stain condition indicates that Himalayas block is still the area with the most intensive tectonic activity and it shortens in the NS direction at the rate of 15.2±1.5 mm/a. Tianshan block ranks the second and it shortens in the NS direction at the rate of 10.1±0.9 mm/a. At present, the two blocks are still uprising. It can be seen from superficial strain that the Chinese mainland is predominated by superficial expansion. Almost the total area in the eastern part of the Chinese mainland is expanded, while in the western part, the superficial compression and expansion are alternatively distributed from the south to the north. In the Chinese mainland, most EW-trending or proximate EW-trending faults have the left-lateral or left-lateral strike-slip relative movements along both sides, and most NS-trending faults have the right-lateral or right-lateral strike-slip relative movements along both sides. According to the data from GPS measurements the left-lateral strike-slip rate is 4.8±1.3 mm/a in the central part of Altun fault and 9.8±2.2 mm/a on Xianshuihe fault. The movement of the fault along the block boundary has provided the condition for block movement, so the movements of the block and its boundary are consistent, but the movement levels of the blocks are different. The statistic results indicate that the relative movement between most blocks is quite significant, which proves that active blocks exist. Himalayas, Tianshan, Qiangtang and SW Yunnan blocks have the most intensive movement; China-Mongolia, China-Korea (China-Korea), Alxa and South China blocks are rather stable. The mutual action of India, Pacific and Philippine Sea plates versus Eurasia plate is the principal driving force to the block movement in the Chinese mainland. Under the NNE-trending intensive press from India plate, the crustal matter of Qingzang plateau moves to the NNE and NE directions, then is hindered by the blocks located in the northern, northeastern and eastern parts. The crustal matter moves towards the Indian Ocean by the southeastern part of the plateau.